Description
Genuine Ludwigia crassa Ammonite Fossil
This carefully chosen fossil is a genuine Ludwigia crassa ammonite from Calvados, France, with its recorded geological information placing it within the Aalenian Stage of the Middle Jurassic. The specimen is associated with the Marnes de Dives Formation and represents an extinct marine cephalopod from the ancient seas that once covered much of north-western Europe.
The photograph shows the actual fossil specimen you will receive, rather than a representative example. Its natural shell preservation, colour variations, remaining ornamentation, attached matrix and individual geological characteristics can therefore be examined before purchase. Full sizing and scale information can be seen in the accompanying photograph.
Aalenian Middle Jurassic Ammonite
The Aalenian is the earliest stage of the Middle Jurassic and records a major period in the development and diversification of ammonites. During this interval, the region that now forms northern France was influenced by extensive marine environments connected to the wider European Jurassic seas.
Fine mud, carbonate sediment and the remains of marine organisms accumulated across the seabed. Ammonite shells could settle onto the sea floor following the animal’s death, where rapid burial protected some examples from complete destruction. Over immense periods of geological time, compaction and mineral-rich groundwater transformed the surrounding sediment into rock and preserved the shells as fossils.
Ammonites are particularly important to Jurassic geology because many species evolved rapidly and had broad geographical distributions. Distinctive ammonite assemblages can therefore help geologists compare and correlate marine rock layers from different localities.
Ludwigia Shell Form and Ornamentation
Ludwigia is a recognised genus of graphoceratid ammonites characterised by a planispirally coiled shell. The whorls developed around a central umbilicus, with each successive growth stage forming a larger portion of the shell.
Species within the genus often have a compressed to moderately robust shell profile. Their flanks may display curved, flexuous or gently sweeping ribs that change in strength and spacing as the animal grows. The outer margin of the shell, known as the venter, is commonly narrow and may possess a defined keel, giving the ammonite a streamlined outline.
The name crassa refers to a comparatively substantial or thickened form. A specimen identified as Ludwigia crassa may therefore show more robust proportions than especially slender members of the genus, although its visible appearance will depend on growth stage, fossilisation and preparation.
The original shell was divided internally by walls called septa. These separated a series of chambers forming the phragmocone, while the living animal occupied the final body chamber. By regulating liquid and gas within the older chambers, the ammonite could control its buoyancy and move through the Jurassic water column.
Scientific Classification and Geological Details
Fossil type: Ammonite
Scientific name: Ludwigia crassa
Family: Graphoceratidae
Superfamily: Hildoceratoidea
Order: Ammonitida
Geological period: Jurassic
Geological epoch: Middle Jurassic
Recorded stage: Aalenian
Recorded formation: Marnes de Dives Formation
Locality: Calvados, France
The Graphoceratidae were an important family of Jurassic ammonites that included several genera with compressed shells, defined venters and distinctive rib patterns. Ludwigia is associated with Aalenian marine strata and is well represented within the fossil record of western Europe.
Marine Environment of Jurassic Calvados
Jurassic Calvados formed part of a sedimentary basin influenced by open marine conditions. The area supported a varied ecosystem containing ammonites, belemnites, bivalves, gastropods and other invertebrates.
Sediments deposited in these marine settings could include clay-rich mud, marl and carbonate material. Conditions varied through time as water depth, currents, oxygen levels and sediment supply changed. Some fossil horizons accumulated slowly, allowing shells and skeletal remains to become concentrated on the seabed before final burial.
The Marnes de Dives is principally known as a marl-rich marine unit containing fossil-bearing horizons, reflecting deposition in a muddy coastal environment open to offshore waters and continental sediment input.
Natural Fossil Preservation
Any attached rock matrix, incomplete shell areas, mineral-filled sections, surface weathering, small fractures or variations in colour are natural characteristics of a genuine fossil. These features developed through burial, mineralisation, geological pressure and later exposure of the host rock.
The original aragonitic shell may have been altered, replaced or dissolved during fossilisation, leaving preserved shell material, an internal mould or a combination of both. This geological process gives every ammonite its own distinctive texture and appearance, ensuring that no two naturally preserved specimens are exactly alike.
Collectable French Jurassic Fossil
This Ludwigia crassa ammonite fossil would make an excellent addition to a collection of French fossils, Calvados ammonites, Aalenian fossils, Middle Jurassic specimens or fossil cephalopods. Its recorded scientific identification and locality also make it suitable for a natural history display, geological study collection, fossil cabinet, office or educational setting.
This is a 100% genuine fossil specimen and includes a Certificate of Authenticity generic card with a lifetime guarantee. The fossil has been individually selected for its collectable qualities, and the photograph shows the exact specimen that will be supplied.
Full sizing please see photo.
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